Advanced Lateral Stability Analyses for Lightweight Pipelines on Clay: A Case Study Available to Purchase

In 2007 DNV issued the new recommended practice DNV-RP-F109 On-Bottom Stability Design of Submarine Pipelines which replaced RP-E305 from 1988 with the same title. The new DNV-RP-F109 describes three different design approaches; full dynamic analysis, absolute static stability, and the generalized method with design curves for virtually stable pipes (allowing up to 0.5 diameters lateral displacement) and for up to 10 pipe diameters displacement in an extreme storm condition. DNV-RP-F109 recommends limiting the sum of the lateral displacement in the temporary condition and during operation to 10 diameters. For larger displacements one should perform a full dynamic analysis and special considerations with respect to bending and fatigue should be made. This paper is concerned with the consequences of exceeding the 10-diameter displacement criterion described in DNV-RP-F109, and how to use different methodologies in accordance with DNV-RP-F109 to ensure limited lateral displacements, acceptable environmental loads/strains and limited/acceptable fatigue damage accumulation. The methodologies covered in this paper include advanced assessments of passive resistance in soil, and account for increased vertical penetration due to laying and lateral fixation of the pipe at regular intervals. For the laterally restricted pipe, studies on reaction forces and reaction moments are made in addition to fatigue estimations at the points of maximum local longitudinal stress. Variations in environmental conditions, soil conditions and levels of effective axial force have also been considered.